Diffusers are known in which the liquid-conveying means are constituted by a rod or wick of porous material dipping into a flask containing the liquid to be diffused and raising it by capillary action. In other diffusers, the liquid-conveying means are constituted by a simple tube dipping into the liquid and operating by gravity or by pressure or by vacuum or by ventilated dropping.
These diffusers suffer from various drawbacks due to the fact that they are not capable of avoiding carbonization and overheating which would otherwise crack or oxidize the active principles of the liquid to be diffused. In addition, e.g. because the wick saturates, such diffusers are not capable of ensuring that the evacuation process takes place regularly at a constant speed, which is necessary to ensure that the fragrant properties of the original liquid are maintained at the desired level.
Other diffusers make use of propellant gases of the fluorohydrocarbon type, for example. Such systems are controversial by virtue of fears about their effect on the environment. A good indication of current concerns is given by diffusers that use a piston pump controlled by an excentric driven by an electric motor (U.S. Pat. No. 4,189,098). These devices are expensive and inadequate for replacing the use of dissolved propellant gases.